Epoxidation of propylene utilizing molybdenum-containing catalyst solutions

ABSTRACT

A process for the epoxidation of propylene utilizing as the catalyst a molybdenum-containing epoxidation catalyst solution prepared by heating molybdenum powder with a stream containing unreacted tertiary butyl hydroperoxide used in the epoxidation process as the oxidizing agent and polyhydric compounds of from 200 to 300 molecular weight and having from four to six hydroxyl groups per molecule, the polyhydric compound being formed as a by-product in the epoxidation process.

United States Patent Sorgenti [54] EPOXIDATION OF PROPYLENE UTILIZINGMOLYBDENUM- CONTAINING CATALYST SOLUTIONS 72 Inventor: Harold A.Sorgenti, Olympia Fields, in.

[73] Assignee: Atlantic Richfield Company, New York,

[22] Filed: Aug. 31, 1970 [21] Appl.No.: 68,595

Related U.S. Application Data [60] Division of Ser. No. 812,845, Apr. 2,1969, Pat. No. 3,573,226, which is a continuation-in-part of Ser. No.647,941, June 22, 1967, abandoned.

[52] U.S. CI ..260/348.5 L, 252/430, 252/431 [51] Int. Cl. ..C07d 1/12,C07d 1/08 [58] Field of Search ..260/348.5 L

[151 3,666,777 51 'May 30, 1972 [56] References Cited UNITED STATESPATENTS 3,351,635 11/1967 Kollar ..260/348.5 3,434,975 3/ 1969 Sheng etal. ..252/43l 3,480,563 1 1/1969 Bonetti et a1. ..252/431 PrimaryExaminer-Norma S. Milestone Atlomey-Robert R. Cochran and John D.Peterson ABSTRACT 2 Claims, No Drawings RELATED APPLICATIONS Thisapplication is a division of my application Ser. No. 812,845, filed Apr.2, 1969, entitled MOLYBDENUM-CON- TAINING CATALYST SOLUTIONS AND METHODOF MAKING AND USING SAME, and now US. Pat. No. 3,573,226, which in turnis a continuation-in-part of my application Ser. No. 647,941, filed June22, 1967, entitled MOLYBDENUM-CONTAINING CATALYST SOLUTIONS AND METHODOF MAKING AND USING SAME, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to a method for the production ofmolybdenum-containing catalyst solutions by incorporating metallicmolybdenum in the distillate bottoms of an epoxidation reaction productand thereafter heating the mixture. It also relates to the catalystsolution made by this method and to the olefin epoxidation processutilizing such method and catalyst solution.

2. Prior Art No prior art is known which relates to the instant methodof producing molybdenum-containing catalyst solutions and to thecatalyst solution produced thereby. The closest art known to theinventor is U.S. Pat. No. 3,434,975 (1969) to Sheng et al., entitledMolybdenum-Containing Catalyst and Method for the Preparation Thereof"wherein there is shown a method of making a molybdenum-containingepoxidation catalyst by reaction molybdenum metal with a peroxy compoundsuch as an organic hydroperoxide in the presence of a C C saturatedmonohydric or dihydric alcohol.

It is shown in this application that methanol gives superior resultswith respect to the quantity of molybdenum which is solubilized and asthe molecular weight of the alcohol increases the amount of molybdenumwhich is solubilized decreases rather markedly such that with tertiarybutyl alcohol only a very small amount of molybdenum is solubilized.

Similarly, it is stated that ethylene glycol is efi'ective insolubilizing the molybdenum when used in combination with thehydroperoxide and while propylene glycol also may be used the highermolecular weight dihydric compounds such as a C diol are substantiallyineffective.

The present invention differs from this method in that the molybdenummetal is treated with a bottoms fraction of an epoxidation reactionmixture which is catalyzed by a molybdenum-containing catalyst andwherein an organic hydroperoxide is utilized as the oxidizing agent. Thebottoms fraction is obtained by distilling the reaction mixture toremove unreacted olefin, the olefin oxide and most of the alcohol whichis produced in the epoxidation reaction by the reduction of thecorresponding hydroperoxide. The bottoms fraction contains undecomposedhydroperoxide, higher boiling by-products from the epoxidation reactionand used molybdenum catalyst.

The higher boiling by-products from the epoxidation reaction have beenfound to be high molecular weight polyhydric compounds and since theonly low molecular weight alcohol present in the bottoms fraction is thealcohol produced from the hydroperoxide which is very poor forsolubilizing molybdenum and since there are little if any C C glycols inthe bottoms fraction it is completely unexpected that the high molecularweight polyhydric compounds can be utilized in combination with theorganic hydroperoxide to solubilize the molybdenum and produce amolybdenum catalyst solution.

The catalysts of the instant invention are suitable for the epoxidationof olefinically unsaturated compounds utilizing an organic hydroperoxideas the oxidizing agent. In particular, they are useful in accordancewith the method set forth in detail in Belgian Pat. No. 674,076, datedJune 20, 1966.

SUMMARY OF THE INVENTION In accordance with the present inventionmetallic molybdenum is reacted with a bottoms fraction obtained as abyproduct from the epoxidation reaction of an olefin with an organichydroperoxide in the presence of a molybdenum-containing catalyst. Thereis obtained by this reaction a molybdenum-containing catalyst solutionwhich can be used as the catalyst either in the same epoxidationreaction which produced the original bottoms fraction, i.e. a recycleoperation, or in any epoxidation reaction wherein an olefinicallyunsaturated compound is reacted with an organic hydroperoxide to producean oxirane compound.

It is an object of this invention, therefore, to provide a method forthe production of economical and efficient molybdenum-containingcatalyst solutions useful in the production of oxirane compounds fromolefinically unsaturated compounds.

It is another object of this invention to provide a method for theproduction of molybdenum-containing catalyst solutions from a bottomsfraction of an epoxidation process.

It is another object of this invention to provide a method for theepoxidation of olefins wherein at least a portion of a bottoms fractionof the olefin epoxidation reaction product is reacted with metallicmolybdenum to produce a catalyst solution which is recycled to theolefin epoxidation step.

It is another object of this invention to provide molybdenum-containingcatalyst solutions useful in the production of oxirane compounds fromolefinically unsaturated compounds.

Other objects of the invention will be apparent from the description ofthe preferred embodiments and from the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS but particles below about 0.1millimeter are somewhat more 7 preferable, but it will be clear thatthis is not a limiting feature of the invention. Other forms of themetal such as sheet, strips, rods, lumps and the like require longerreaction times to obtain the molybdenum solution and consequently arenot preferred.

The epoxidation reaction from which the bottoms fraction is obtained maybe, in general, one wherein an olefinically unsaturated compound isreacted with an organic hydroperoxide in the presence of a solublemolybdenum catalyst.

in a preferred embodiment, however, the reaction of propylene withtertiary butyl hydroperoxide in the presence of a molybdenum catalystsolution is used as the source of the reaction mixture bottoms. In thisreaction there is produced a reaction mixture consisting of unreactedpropylene, unreacted tertiary butyl hydroperoxide, propylene oxideproduct, tertiary butyl alcohol which is produced by the reduction ofthe tertiary butyl hydroperoxide, acidic compounds, other peroxycompounds, high molecular weight polyhydric compounds in the range of200 to 300 molecular weight and used molybdenum catalyst.

The propylene epoxidation process is carried out at a temperature in therange of from about F. to 300 F. and under pressures in the range offrom 300 psig to 1,000 psig and preferably at temperatures in the rangeof from about 220 F. to 280 F. and under pressures preferably from 500psig to 800 psig. In general a catalyst concentration ranging between 20ppm and 1,000 ppm of molybdenum by weight based on the weight ofpropylene-free liquid in the reaction is suitable for carrying out thereaction while a concentration in the range of 50 ppm to 500 ppm ofmolybdenum by weight based on the weight of the propylene-free liquid ispreferred.

This reaction mixture is distilled to remove the propylene, propyleneoxide and most of the tertiary butyl alcohol. The bottoms fraction thuscontains only a small amount of the tertiary butyl alcohol together withthe unreacted tertiary butyl hydroperoxide, acidic compounds, polyhydriccompounds and used catalyst.

In general the amounts of these materials in the bottoms fraction canvary quite widely depending upon the manner in which the reaction iscarried out. In most instances the tertiary butyl hydroperoxide willrange between 5 weight percent and 30 weight percent of the fraction,the tertiary butyl alcohol from 25 weight percent to 55 weight percent,the high molecular weight polyhydric compounds from weight percent to 55weight percent and the acidic and other peroxy compounds from 4 weightpercent to 8 weight percent.

To this residual fraction molybdenum powder is added and the mixtureheated to a temperature in the range between 140 F. and the refluxtemperature (at atmospheric pressure) of the mixture for a time in therange of 0.5 to 7 hours with from 0.5 to 2.0 hours usually beingsufficient. In general, the reflux temperature of the mixture isapproximately 190 F., however, if there is a high proportion of highboiling compounds in the bottoms fraction the reflux temperature may beas high as 198 F. to 200 F. or more. The reaction mixture is filteredand the resultant filtered solution is the molybdenum catalyst solutionwhich is useful in catalyzing the oxidation of olefinically unsaturatedcompounds by an organic hydroperoxide oxidizing agent.

In a particularly preferred embodiment of the invention this catalystsolution is recycled to the propylene epoxidation step. When recycle isemployed only a portion of the total bottoms fraction is required forproducing additional catalyst for recycle. Although the entire bottomsfraction can be used to make catalyst, if only that portion is usedwhich is required to produce sufficient catalyst solution for recycle,build-up of high molecular weight polyhydric compounds in theepoxidation reaction is prevented.

The amount of the bottoms fraction required is that which will providethe molybdenum concentration in the epoxidation reaction which has beenset forth, i.e. a concentration ranging between 20 ppm and 1,000 ppm ofmolybdenum by weight based on the weight of propylene-free liquid in thereaction. In order to obtain a catalyst solution which will provide thisnecessary concentration it has been found that it is necessary to have aweight ratio of molybdenum metal to hydroperoxide in the bottomsfraction in the range of from about 1:5 to I240 with a ratio of 1:10 to1:30 being somewhat more preferred. In addition, it has also been foundthat the weight ratio of molybdenum powder to the high molecular weightpolyhydric compounds should be between about 1:5 and 1:200 withexcellent results being obtained at ratios between 1:15 and 1:30. Sinceboth the hydroperoxide and high molecular weight polyhydric compoundsare necessary to solubilize the molybdenum powder to make the catalystsolution the weight ratio of molybdenum to each of these components hasbeen specified since the ratio of hydroperoxide to high molecular weightpolyhydric compounds can vary in the bottoms fraction in accordance withthe reaction conditions being employed in the epoxidation reaction. Ingeneral, they will be within the ranges which have been set forth.

Thus, for example, if the molybdenum in the catalyst solution were at aconcentration of 2,500 ppm by weight and it was desired to maintain theepoxidation reaction at a catalyst concentration of 100 ppm in thepropylene-free liquid then the amount of catalyst solution would beabout 0.04, the amount of the propylene-free liquid. Generally, theseconcentrations are expressed in parts by weight. Likewise, if thecatalyst solution were made to contain l0,000 ppm and it was desired tohave a catalyst concentration of I00 ppm in the propylene-free liquid ofthe epoxidation reaction, then the amount of catalyst liquid requiredwould be about 0.01, the amount of the propylene-free liquid in thereaction.

The liquid in the epoxidation reaction mixture is preferably expressedon a propylene-free basis for the obvious reason that the amount ofpropylene will vary with temperature and pressure utilized in thereaction since propylene is a gaseous compound at ambient conditions.

The following examples are provided to illustrate the invention ingreater detail and to illustrate preferred embodiments of the invention.it will be understood, however, that these examples are not to beconstrued as limiting the invention thereto.

EXAMPLE I A bottoms fraction was obtained from an epoxidation reactionmixture wherein propylene was converted to propylene oxide utilizingtertiary butyl hydroperoxide as the oxidizing agent in the presence of amolybdenum-containing catalyst solution. The bottoms fraction wasobtained by distilling the reaction mixture to remove unreactedpropylene, the propylene oxide product and some of the tertiary butylalcohol produced by reduction of the tertiary butyl hydroperoxide. Thebottoms fraction was analyzed and found to contain 26 weight percentunreacted tertiary butyl hydroperoxide, 48 weight percent tertiary butylalcohol, l.2 weight percent water, 6.0 weight percent acidic compounds,5.2 weight percent allyl tertiary butyl peroxide, 1.2 weight percentisobutyl alcohol, 0.3 weight percent other alcohols, 12.1 weight percenthigh molecular weight polyhydric compounds and approximately 700 ppmmolybdenum in the form of the used catalyst. The high molecular weightpolyhydric compounds as they will be referred to hereinafter and in theclaims have a molecular weight in the range of from about 200 to- 300with an approximate elemental analysis of carbon 59 weight percent,hydrogen 10 weight percent and oxygen 31 weight percent. This analysiscorresponds to a formula ranging from C I-I Oto (E i-[ 0 indicatingthese compounds have from four to six hydroxyl groups per molecule.

To each I00 grams of this bottoms fraction was added 0.8 grams ofpowdered molybdenum. This mixture was refluxed for 1 hour and thereafterfiltered. The filtrate when analyzed and after correcting for theoriginal quantity of molybdenum present in the bottoms, showed thatsubstantially all of the molybdenum which had been added was dissolved.This demonstrates the surprising discovery of this invention; namely,that the high molecular weight polyhydric compounds in the bottomsfraction are completely effective in solubilizing molybdenum to producea molybdenum catalyst solution.

This catalyst was tested in batch equipment for the epoxidation ofpropylene and compared with standard runs made under the same conditionsutilizing a standard soluble molybdenum catalyst prepared by reactingmolybdenum metal with fresh propylene glycol and fresh tertiary butylhydroperoxide with tertiary butyl alcohol as the solvent, i.e. thecatalyst of the afore-mentioned application Ser. No. 516,778. A reactiontemperature of 265 F. a pressure of 650 psig, a reaction time of 1 hour,a catalyst concentration of ppm based on the total volume of reactantsand a propylene concentration of 45 weight percent was employed.

In four runs the percent conversions based on moles of hydroperoxideconverted per mole of hydroperoxide charged were 87, 85, 94 and 96. Inthese same four runs the percent selectivities based on moles ofpropylene oxide produced per mole of hydroperoxide converted were,respectively, 89.5, 83 87 and 82.5.

In the two standard runs made for comparison purposes the conversion was86 percent and 95 percent with selectivity of 87.5 percent and 85percent. These data demonstrate that the catalyst solution of theinstant invention is equivalent to soluble molybdenum catalysts.

EXAMPLE ll A number of other catalysts were prepared by reactingmolybdenum powder with the bottoms fraction resulting from theconversion of propylene to propylene oxide utilizing tertiary butylhydroperoxide as the oxidizing agent and the molybdenum catalystsolution prepared from propylene glycol and tertiary butylhydroperoxide. It will be understood, however, any other solublemolybdenum catalyst such as molybdenum naphthenate, molybdenumhexacarbonyl, etc. may be used to carry out the initial epoxidationwhich produces the high molecular weight polyhydric compounds. Theamount of tertiary butyl hydroperoxide in the bottoms fractions wasvaried from 13 weight percent to 35 weight percent along with the amountof tertiary butyl alcohol which was varied from about 25 weight percentto 55 weight percent with the amounts of high boiling, high molecularweight polyhydric compounds varying from about weight percent to about53 weight percent. In addition to varying the quantities of reactants,reaction times from 0.5 to 7 hours were employed with temperaturesranging from l40 F. to reflux temperatures. In each case the amount ofpowdered molybdenum added was 0.8 grams per 100 grams of bottoms inorder to obtain a variation in the ratio of molybdenum metal tohydroperoxide and to the high molecular weight polyhydric compounds. inall cases substantially all of the molybdenum was dissolved to producean effective molybdenum epoxidation catalyst solution.

It was found that all of these catalysts are completely effective bothwith respect to conversion and selectivity for catalyzing the propyleneoxidation to produce propylene oxide with tertiary butyl hydroperoxide.

Since the bottoms fraction contains a molybdenum catalyst which has beenused for the epoxidation reaction, the process wherein additionalmolybdenum is reacted with the bottoms fraction can be considered one offortification followed by recycle. Since the epoxidation of propylenecan be carried out in a continuous system this fortification process isparticularly suitable for producing catalyst solutions which can berecycled to the process.

EXAMPLE III in order to demonstrate the feasibility of utilizing themolybdenum-containing catalyst solutions of this invention in acontinuous olefin epoxidation process a catalyst solution was preparedin the manner set forth in Example I from a propylene epoxidationreaction product bottoms fraction of a propylene epoxidation processsimilar to that described in EX- ample l. The catalyst solution thusprepared had a molybdenum concentration of 5,600 ppm. This solution wasintroduced into a continuous propylene epoxidation process wherein thereaction conditions were a temperature of 250 F a pressure of 600 psig,a flow rate of ccs per hour of tertiary butyl hydroperoxide and ccs perhour of propylene. There was maintained a molybdenum concentration of330 ppm based on the quantity of propylene-free liquid in the reaction.There was obtained a conversion of 81 percent based on moles ofhydroperoxide converted per mole of hydroperoxide charged and aselectivity of 75 percent based on moles of propylene oxide produced permole of hydroperoxide charged. This experiment shows that the catalystproduced in accordance with this invention may be produced from andrecycled to a continuous process.

I claim:

I. A process for the epoxidation of propylene which comprises contactingpropylene with tertiary butyl hydroperoxide at a temperature in therange of from F. to 300 F. and pressures in the range of from 300 psigto 1,000 psig in the presence of a molybdenum catalyst solution saidmolybdenum concentration ranging between 20 ppm and 1,000 ppm based onthe liquid in said reaction free of propylene, to produce a reactionproduct containing unreacted propylene, propylene oxide, tertiary butylalcohol, unreacted tertiary butyl hydroperoxide and polyhydriccompounds, having a molecular weight in the range from about 200 to 300and having from four to six hydroxyl groups per molecule, said compoundsbeing produced during said propylene epoxidation process, distilling toremove from the reaction product the unreacted propylene, the propyleneoxide and a major proportion of the tertiary butyl alcohol, leaving abottoms fraction containing said unreacted tertiary butyl hydroperoxide,a minor proportion of said tertiary butyl alcohol and said polyhydriccompounds, adding powdered metallic molybdenum to at least a portion ofsaid bottoms fraction from the distillation, said bottoms fraction beingin an amount required to produce sufficient catalyst solution forrecycle to said contacting step, said powdered metallic molybdenum beingadded in an amount such that the weight ratio of said molybdenum metalto said hydroperoxide is in the range of from about 1:5 to 1:40 and theweight ratio of said molybdenum metal to said polyhydric compounds beingin the range between about 1:5 to 1:200, heating to a temperature in therange of from 140 F. to the reflux temperature of said bottoms fractionfor a time ranging from 0.5 to 7.0 hours to produce amolybdenum-containing catalyst solution to the propylene epoxidationstep.

2. The process according to claim 1 wherein the propylene epoxidationstep is carried out at a temperature in the range of from 250 F. to 290F. and under pressures in the range of from 500 psig to 800 psig.

2. The process according to claim 1 wherein the propylene epoxidationstep is carried out at a temperature in the range of from 250* F. to290* F. and under pressures in the range of from 500 psig to 800 psig.